GPT-5.6-Sol skips ClickUp Get task and can fabricate an answer while Terra/Luna invoke it

Summary

In Codex Desktop on Windows, GPT-5.6-Sol can fail to invoke ClickUp's Get task action even when the ClickUp app is explicitly attached to a fresh task. It may return a plausible answer without any ClickUp tool event; when challenged, it acknowledged that it had not made the call and had fabricated the answer. In another fresh task, it reported that ClickUp Get task was not exposed.

The same ClickUp connection and request succeed with GPT-5.6-Terra and GPT-5.6-Luna: they invoke ClickUp → Get task and then respond based on the task.

Steps to reproduce

1. In Codex Desktop for Windows, start a fresh task with GPT-5.6-Sol.
2. Explicitly attach the installed ClickUp app.
3. Send a request such as:

``
Use ClickUp's Get task action now for <a valid ClickUp custom task ID>.
Do not respond until the tool call has completed.
Then reply only: Easy, Medium, or Hard.
``

1. Observe that Sol may respond (for example, Hard) with no ClickUp → Get task tool event.
2. Ask how it determined the answer. It can acknowledge that it did not make the ClickUp call and fabricated the rating.
3. Repeat in another new Sol task. It may instead say the ClickUp Get task action is not exposed.
4. Repeat the same test with Terra or Luna against the same ClickUp connection. They invoke Get task successfully.

Expected behavior

With ClickUp explicitly attached and an explicit Get task request, Sol should invoke the action before responding. If the tool genuinely is unavailable, it should state that without inventing a result.

Actual behavior

Sol can skip the tool call and fabricate an answer, or claim that Get task is not exposed. The submitter reproduced this across 12 fresh Sol tasks, while Terra and Luna succeeded with the same ClickUp connection.

Environment

• ChatGPT Pro subscription
• Codex Desktop for Windows (latest version) // Also tried the same process in Codex CLI
• ClickUp app explicitly attached
• Models compared: GPT-5.6-Sol (fails), GPT-5.6-Terra and GPT-5.6-Luna (succeed)
• Exact task ID can be provided privately if useful

Related issue

This appears distinct from #32710. That issue concerns a ClickUp comment-write tool whose backend returns Tool ... not found; here, the read action Get task works with Terra/Luna but is not invoked or exposed for Sol.

Screenshots

GPT-5.6-Luna:
<img width="1918" height="1020" alt="Image" src="https://github.com/user-attachments/assets/5695e7d6-244d-468b-85e5-fe31548554d6" />

GPT-5.6-Sol:
<img width="874" height="685" alt="Image" src="https://github.com/user-attachments/assets/2428ccf8-e0c5-40cb-8d84-5bc5fb4a6ff1" />

<img width="1013" height="595" alt="Image" src="https://github.com/user-attachments/assets/19aa1b1b-4ea5-44bf-85e1-e99cd0203358" />